T&T: Can you over zinc a boat?

[Robert Kassal]

My diver thinks our boat is over zinc'd. This is a 48 foot boat with long
shafts and it has three zinc's per shaft, one each on the rudders and trim
tabs. The latter are probably a size too big.

During the barnacle removal, the diver hit a 5/16" SS bolt (that attaches a SS
swim platform support to a SS transom bracket) and it broke at the head. The
post mortem shows a large pit into the bolt right at the head. I know this
bolt has only been in the water 8 months.Could this be the result of too much
zinc?

Bob